The present invention relates to a black magnetic toner, and more particularly, to black a black magnetic toner using magnetic composite particles, which is not only excellent in fluidity and blackness, but also small in reduction of electric resistance and, therefore, can realize a high image quality and a high copying speed, and black magnetic composite particles which not only show an excellent dispersibility in a binder resin due to less amount of carbon black fallen-off from the surface of each particle, but also have an excellent fluidity and blackness.
As one of conventional electrostatic latent image-developing methods, there has been widely known and generally adopted a so-called one component system development method of using as a developer, a magnetic toner comprising composite particles prepared by mixing and dispersing magnetic particles such as magnetite particles in a resin, without using a carrier.
The conventional development methods of using one-component magnetic toner have been classified into CPC development methods of using a low-resistance magnetic toner, and PPC development methods of using a high-resistance magnetic toner.
In the CPC methods, the low-resistance magnetic toner used therefor has an electric conductivity, and is charged by the electrostatic induction due to electric charge of the latent images. However, since the charge induced on the magnetic toner is lost while the magnetic toner is transported from a developing zone to a transfer zone, the low-resistance magnetic toner is unsuitable for the PPC development method of using an electrostatic transfer method. In order to solve this problem, there have been developed the insulated or high resistance magnetic toners having a volume resistivity as high as not less than 1014 xcexa9xc2x7cm.
As to the insulated or high-resistance magnetic toner, it is known that the developing characteristics thereof are affected by magnetic particles exposed to the surface of the magnetic toner, or the like.
Recently, with the high image quality such as high image density or high tone gradation, or with the high copying speed of duplicating machines, it has been strongly demanded to further enhance characteristics of the insulted or high-resistance magnetic toners as a developer, especially a fluidity thereof.
With respect to such demands, in Japanese Patent Application Laid-Open (KOKAI) No. 53-94932(1978), there has been described xe2x80x9cthese high-resistance magnetic toners are deteriorated in fluidity due to the high electric resistance, so that there arises such a problem that non-uniformity of developed images tend to be caused. Namely, although the high-resistance magnetic toners for PPC development method can maintain necessary charges required for image transfer, the magnetic toners are frictionally charged even when they are present in other steps than the transfer step, where the magnetic toners are not required to be charged, e.g., in a toner bottle or on the surface of a magnetic roll, or also slightly charged by mechano-electrets during the production process of these magnetic toners. Therefore, the magnetic toners tend to be electrostatically agglomerated, resulting in deterioration of fluidity thereofxe2x80x9d, and xe2x80x9cIt is an another object of the present invention to provide a high-resistance magnetic toner for PPC development method which is improved in fluidity, can be prevented from causing non-uniformity of developed images, and has an excellent image definition and tone gradation, thereby obtaining high-quality copies by indirect copying methodsxe2x80x9d.
In recent years, with the reduction in particle size of the insulated or high-resistance magnetic toners, it has been increasingly required to enhance the fluidity thereof.
With respect to such a fact, in xe2x80x9cComprehensive Data Collection for Development and Utilization of Toner Materialsxe2x80x9d published by Japan Scientific Information Co., Ltd., page 121, there has been described xe2x80x9cWith extensive development of printers such as ICP, a high image quality has been required. In particular, it has been demanded to develop high-precision or high-definition printers. In Table 1, there is shown a relationship between definitions obtained by using the respective toners. As is apparent from Table 1, the smaller the particle size of wet toners, the higher the image definition is obtained. Therefore, when a dry toner is used, in order to enhance the image definition, it is also required to reduce the particle size of the toner . . . . As reports of using toners having a small particle size, it has been proposed that by using toners having a particle size of 8.5 to 11 xcexcm, fogs on a background can be improved and toner consumption can be reduced, and further by using polyester-based toners having a particle size of 6 to 10 xcexcm, an image quality, a charging stability and lifetime of the developer can be improved. However, when such toners having a small particle size are used, it has been required to solve many problems. There are problems such as improvement in productivity, sharpness of particle size distribution, improvement in fluidity, etc.xe2x80x9d.
Further, black magnetic toners widely used at the present time, have been required to show a high degree of blackness and a high image density for line images and solid area images on copies.
With respect to this fact, on page 272 of the above-mentioned xe2x80x9cComprehensive Data Collection for Development and Utilization of Toner Materialsxe2x80x9d, there has been described xe2x80x9cPowder development is characterized by a high image density. However, the high image density as well as the fog density as described hereinafter, greatly influences image characteristics obtainedxe2x80x9d.
There is a close relationship between properties of the magnetic toner and those of the magnetic particles mixed and dispersed in the magnetic toner.
That is, the fluidity of the magnetic toner is largely varied depending upon surface condition of the magnetic particles exposed to the surface of the magnetic toner. Therefore, the magnetic particles themselves have been strongly required to show an excellent fluidity.
The degree of blackness and density of the magnetic toner are also largely varied depending upon the degree of blackness and density of the magnetic particles as a black pigment contained in the magnetic toner.
As the black pigment, magnetite particles have been widely used from the standpoints of magnetic properties such as saturation magnetization or coercive force, low price, color tone or the like. In addition to the magnetite particles, carbon black fine particles may be added. However, in the case where the carbon black fine particles are used in a large amount, the electric resistance is lowered, so that it is not possible to obtain an insulated or high-resistance magnetic toner.
Hitherto, in order to enhance the fluidity of the black magnetic toner, there have been many attempts of improving the fluidity of the magnetite particles mixed and dispersed in the magnetic toner. For example, there have been proposed (1) a method of forming spherical-shaped magnetite particles (Japanese Patent Application Laid-Open (KOKAI) No. 59-64852(1984)), (2) a method of exposing a silicon compound to the surface of magnetite particles (Japanese Patent Publication (KOKOKU) No. 8-25747(1996)), or the like.
Black magnetic particles for black magnetic toner, which have not only an excellent fluidity and blackness, but also an excellent dispersibility in a binder resin, are presently strongly demanded. However, black magnetic particles capable of satisfying all of these requirements have not been obtained yet.
Namely, the above-mentioned spherical magnetite particles show a higher fluidity than those of cubic magnetite particles, octahedral magnetite particles or the like. However, the fluidity of the spherical magnetite particles is still insufficient, and further the blackness is disadvantageously low.
As to the above-mentioned magnetite particles to the surface of which the silicon compound is exposed, the fluidity thereof is also still insufficient, and the blackness thereof is also disadvantageously low.
As a result of the present inventor""s earnest studies for solving the above problems, it has been found that by using as a black magnetic toner, black magnetic composite particles obtained by forming a coating layer composed of at least one organosilicon compound selected from the group consisting of (1) organosilane compounds obtainable from alkoxysilane compounds, (2) polysiloxanes or modified polysiloxanes and (3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds, on the surface of magnetic iron oxide particles having an average particle size of 0.055 to 0.95 xcexcm, and forming a carbon black coat on the formed coating layer such that the amount of the carbon black is 1 to 25 parts by weight based on 100 parts by weight of the said magnetic iron oxide particles, the black magnetic toner can have not only an excellent fluidity and an excellent blackness, but also can show a high-resistance or an insulating property without lowering in the electric resistance. The present invention has been attained on the basis of the finding.
It is an object of the present invention to provide a black magnetic toner, which is not only excellent in fluidity and blackness, but also small in reduction of electric resistance and, therefore, can realize a high image quality and a high copying speed.
It is another object of the present invention to provide black magnetic particles for black magnetic toner, which are not only excellent in fluidity and blackness, but also can show an excellent dispersibility in a binder resin.
To accomplish the aims, in a first aspect of the present invention, there is provided a black magnetic toner comprising: a binder resin, and black magnetic composite particles comprising:
magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95 xcexcm;
a coating layer formed on the surface of the said magnetic iron oxide particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising the said organosilicon compound, in an amount of 1 to 25 parts by weight based on 100 parts by weight of the said magnetic iron oxide particles.
In a second aspect of the present invention, there is provided a black magnetic toner comprising: a binder resin, and black magnetic composite particles comprising:
magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95 xcexcm;
a coat formed on at least a part of the surface of the magnetic iron oxide particles, comprising at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the magnetic iron oxide particles;
a coating layer formed on the coat on the surface of the said magnetic iron oxide particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising the said organosilicon compound, in an amount of 1 to 25 parts by weight based on 100 parts by weight of the said magnetic iron oxide particles.
In a third aspect of the present invention, there are provided black magnetic composite particles comprising:
magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95 xcexcm;
a coating layer formed on the surface of the said magnetic iron oxide particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising the said organosilicon compound, in an amount of 1 to 25 parts by weight based on 100 parts by weight of the said magnetic iron oxide particles.
In a fourth aspect of the present invention, there are provided black magnetic composite particles comprising:
magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95 xcexcm;
a coat formed on at least a part of the surface of the magnetic iron oxide particles, comprising at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the magnetic iron oxide particles;
a coating formed on the coat of the surface of the said magnetic iron oxide particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising the said organosilicon compound, in an amount of 1 to 25 parts by weight based on 100 parts by weight of the said magnetic iron oxide particles.
In a fifth aspect of the present invention, there are provided black magnetic composite particles comprising:
maghemite particles having an average particle diameter of 0.055 to 0.95 xcexcm;
a coating layer formed on the surface of the said maghemite particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising the said organosilicon compound, in an amount of 1 to 25 parts by weight based on 100 parts by weight of the said maghemite particles.
In a sixth aspect of the present invention, there are provided black magnetic composite particles comprising:
maghemite particles having an average particle diameter of 0.055 to 0.95 xcexcm;
a coat formed on at least a part of the surface of the maghemite particles, comprising at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the maghemite particles;
a coating formed on the coat of the surface of the said maghemite particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising the said organosilicon compound, in an amount of 1 to 25 parts by weight based on 100 parts by weight of the said maghemite particles.
In a seventh aspect of the present invention, there is provided a method of mixing a binder resin with black magnetic composite particles for production of a black magnetic toner, which black magnetic composite particles comprise:
magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95 xcexcm;
a coating formed on the surface of the said magnetic iron oxide particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising the said organosilicon compound, in an amount of 1 to 25 parts by weight based on 100 parts by weight of the said magnetic iron oxide particles.